1. Technical Field
This invention relates generally to SPECT and CT imaging. Specifically, it relates to registering SPECT images and CT images of the same patient regions, and “zipping” together SPECT images of different portions of a whole body scan to provide a single whole body image.
2. Background of the Invention
When taking whole body Single Photon Emission Computed Tomography (“SPECT”) and Computed Topography (“CT”) scans, in many machines the detector's field of view (“FOV”) is limited. It is therefore often necessary to take several separate scans for SPECT, which overlap in the z direction (see FIG. 1), at two or more different positions with respect to a patient. These separate scans must then be “zipped” or appended together after reconstruction.
When such zipping takes place, it is usually impossible to determine the proper zipping position in the overlapping region where zipping occurs, in the z direction (see FIG. 1). When two adjacent images are so overlapped, the proper dividing line could be anywhere in the overlapping region. Presently there are no satisfactory methods to determine this position and to zip the two images together based either on relative bed positions or on image positions.
Even in cases where the zipping position can be approximated, i.e. when the full reconstruction range is used in the overlapping region, other factors may hinder a satisfactory zipped whole body image. These factors may include: bed deflection, patient motion, and image edge handling in 3D reconstruction algorithms with CT attenuation correction.
In many current methods, image registration (i.e., between the SPECT and CT images) and zipping (i.e., of two SPECT images of overlapping adjacent patient regions) are done completely separately. Auto-zipping is done after the multiple whole body SPECT images have been individually registered with the CT image. The separate registration and zipping processes do not generate satisfactory whole body images.
To solve these problems, it is desired to merge the registration task and the zipping task into a single optimization task.